1. Field of the Invention
The present invention relates to covers, cover bodies and frames, and more particularly to covers for underground structures, cover bodies which are designed to quickly discharge rainwater and dirt collected from the cover bodies and the frames to efficiently prevent pedestrians from slipping and vehicles from skidding, and frames for the cover bodies.
Covers for underground structures herein refers to large iron covers to close openings which lead to buried materials as well as to structural sewerage facilities, manhole covers, covers for house inlets, openable and closable iron covers for common-use tunnels which protect equipment for underground power and communications facilities, iron covers for electric power transmission, iron covers for power distribution, fire hydrant covers functioning as openable and closable doors to connect underground conduits in waterworks systems, covers leading to gas pipes and their accessories from above ground, sluice valve covers, air-valve covers, covers for gas pipes, and water-gauge valves.
2. Description of the Prior Art
It is a known method to form a multiplicity of protruding and recessed patterns on the surfaces of cover bodies and frames of underground structures installed on sidewalks and roadways to prevent pedestrians from slipping and vehicles from skidding in inclement weather.
There are good examples of cover bodies and frames with improved surface patterns for slip and skid prevention disclosed in Japanese Unexamined Utility Model Publication No. 27160/85 and Japanese Utility Model Publication No. 39964/95.
The former concerns a cover body, the surface of which projections of a planar hexagon and planar Y-shaped depressions are alternately and uniformly distributed to form specific patterns, the projections being enclosed by depressions. Such surface patterns are supposed to prevent slipping and skidding regardless of which direction the pedestrians and vehicles advance from. Since the depressions formed around the projections are all connected, they are advantageous in that any dirt collected on the surface thereof can be discharged by using the depressions as cleaning passageways.
The latter method as disclosed in the Gazette presents anti-slip patterns formed on the upper surface of the wall of a flange of a frame. Slip prevention is made by means of each pattern made up of wavy grooves provided peripherally along the flange wall and single holes formed relative to the top and the bottom of the wavy grooves.
However, according to the Utility Model disclosed in Japanese Unexamined Utility Model Publication No. 27160/85, an outer rim is formed around the outer periphery of the cover body. Consequently, even though the depressions as such are all connected, they are surrounded by the outer rim when the cover body is considered as a whole. Further, these depressions merely form a flat surface which is depressed at a uniform depth with respect to the upper surface level, and any difference in level existing between the depressions and the outer rim is on the level of approximately at a right angle or a slope created due to cast trimming, so that guiding accumulations of rainwater and dirt in the depressions to the periphery for discharge thereof will require some degree of human work. It is unreasonable to expect natural discharge thereof with the passage of time.
Another factor is that, since the upper surface of the projections is also a flat surface on a uniform level, rainwater and dirt will remain collected on the upper surface thereof.
In regard to a frame described in Japanese Utility Model Publication No. 39964/95, inasmuch as the anti-slip patterns formed on the upper surface of a flange are depressed relative to the surrounding area, hence constituting closed depressions, rainwater and dirt will likely remain collected, as well.
As described above, the discharge of rainwater and dirt, once accumulated on the surface of the body and the frame in the existing structure, is difficult, and the accumulations thereof tend to remain unchanged. Since such accumulations of rainwater and dirt on the surface act between tires and the surface of the body or frame, for example, as a roller, despite the provision of anti-slip and anti-skid patterns in projections and depressions on the surface thereof, there is the problem of significant loss of effect.